Insulin secretion deficits in a Prader-Willi syndrome β-cell model are associated with a concerted downregulation of multiple endoplasmic reticulum chaperones

• Published in: bioRxiv
• Main Authors: Koppes, Erik A, Johnson, Marie A, Moresco, James J, Luppi, Patrizia, Lewis, Dale W, Stolz, Donna B, Diedrich, Jolene K, Yates, John R, Wek, Ronald C, Watkins, Simon C, Gollin, Susanne M, Park, Hyun J, Drain, Peter, Nicholls, Robert D
• Format: Paper
• Language: English
• Published: Cold Spring Harbor Cold Spring Harbor Laboratory Press 18.06.2022
• Subjects: Beta cells; Chaperones; Children; CRISPR; Dosage compensation; Endoplasmic reticulum; Gene deletion; Genes; Genomes; GRP78 protein; Hyperphagia; Hypoglycemia; Insulin; Insulin secretion; Insulinoma; Neonates; Prader-Willi syndrome; Protein folding; Proteomes; Transcriptomes
• DOI: 10.1101/2021.12.16.473032

Prader-Willi syndrome (PWS) is a multisystem disorder with neurobehavioral, metabolic, and hormonal phenotypes, caused by loss of expression of a paternally-expressed imprinted gene cluster. Prior evidence from a PWS mouse model identified abnormal pancreatic islet development with retention of aged insulin and deficient insulin secretion. To determine the collective roles of PWS genes in β-cell biology, we used genome-editing to generate isogenic, clonal INS-1 insulinoma lines having 3.16 Mb deletions of the silent, maternal (control) or active, paternal PWS-alleles. PWS β-cells demonstrated a significant cell-autonomous reduction in basal and glucose-stimulated insulin secretion. Further, proteomic analyses revealed reduced levels of cellular and secreted hormones, including all insulin peptides and amylin, concomitant with reduction of at least ten endoplasmic reticulum (ER) chaperones, including GRP78 and GRP94. Critically, transcriptomic studies demonstrated that the broad reduction of ER chaperones originated from transcriptional downregulation without corresponding changes for Ins1 and Ins2. In contrast to the dosage compensation previously seen for ER chaperones in Grp78 or Grp94 gene knockouts or knockdown, compensation is precluded by the stress-independent deficiency of ER chaperones in PWS β-cells. Consistent with reduced ER chaperones levels, PWS INS-1 β-cells are more sensitive to ER stress, leading to earlier activation of all three arms of the unfolded protein response. These findings suggest that a chronic shortage of ER chaperones in PWS β-cells leads to a deficiency of protein folding and/or delay in ER transit of insulin and other cargo. In summary, our results illuminate the pathophysiological basis of pancreatic β-cell hormone deficits in PWS, with evolutionary implications for the multigenic PWS-domain, and indicate that PWS-imprinted genes coordinate concerted regulation of ER chaperone biosynthesis and β-cell secretory pathway function. Competing Interest Statement The authors have declared no competing interest. Footnotes * The Abstract (expansion and reworded to highlight all novel findings and relationship to the literature) and Discussion (especially with sub-headings to help the reader with understanding of the significance of our results) have been revised, with minor revisions elsewhere in the main manuscript.